Endoprostheses of this kind are used, in particular, as prostheses for knee joints. Owing to the high loading on knee joints by virtue of the body weight of the patient and owing to the complex movement sequence of said knee joints, they are comparatively more susceptible to dysfunction due to wear or disease. The replacement of a knee joint by an endoprosthesis is a complicated operation which puts stress on the patient. It is therefore desirable to be able to implant the endoprosthesis in a manner which is as straightforward and insusceptible to faults as possible in order to avoid complications.
To this end, a joint endoprosthesis of the kind cited in the introductory part which has a spreadable axial pin has been disclosed (EP 1 381 335 B1). Said joint endoprosthesis comprises a tibial component and a femoral component which are connected to one another in an articulated manner by means of a coupling piece. A bending joint and a rotary joint are formed. The bending joint allows flexion and extension of the knee. To this end, the coupling piece has an axial eye into which an axial pin, which comprises pin stubs, is inserted. The pin stubs are provided with mutually complementary coaxial recesses, with the result that they can be moved toward one another or away from one another in a telescopic manner along their common center axis. For insertion purposes, the pin stubs have to be moved completely toward one another and are therefore located in an installation position in which the pin stubs are retracted into the coupling piece. After the coupling piece has been installed in the mating piece, a hinge fork on the femoral component, said pin stubs are spread and thereby expand into the holes in the hinge fork which are aligned with one another. As a result, the coupling piece is connected to the femoral component in a pivotable manner. This axial pin allows simpler installation, however complications may arise in the event of the pin stubs becoming jammed.